The camera flies majestically towards Dublin, the credits announce a “fillum by Ben Kellett” and we get another chance to ponder one of the age’s more puzzling cultural phenomena.

Mrs Brown’s Boys, the vehicle that propelled Brendan O’Carroll to the top of the heap, is certainly no less old-fashioned than its many critics suggest. The big-screen version really does feature a comedy Oriental, frivolous use of Tourette’s syndrome, and characters who actually say “psst!” when they want to attract attention. One wouldn’t be surprised to hear a few supposedly topical cracks about General de Gaulle or the secession of Rhodesia. Heck, jokes about the Battle of Thermopylae wouldn’t seem out of time in this environment.

For all that, in both its TV incarnation and, now, on film, Mrs Brown’s Boys makes unexpected gestures towards postmodernity. (There you go, Brendan. You can have that one for free, the next time you’re taking a dig at pretentious, elitist critics.) The “fourth wall” is constantly broken as the foul-mouthed matriarch offers sly asides to an indulgent audience. The shots of lights, cameras and circling crew – heck, we’ve risked “postmodern”, so let’s drag in “Brechtian alienation” – suggest a broad cross-dressing sitcom as produced by the Berliner Ensemble around 1950.

D’Movie takes this gag and contorts it into some arresting new angles. Painted backdrops are torn down as, now gifted a proper budget, Mrs Brown takes us to the physical locations that inspired the character. When magical things happen that only happen in cinema, Agnes makes sure to point up the fact. This may very well be the most promiscuously self-conscious meta-movie we have seen since the last Charlie Kaufman project.

None of which is to suggest that Mrs Brown’s Boys D’Movie is any good. It cannot be denied that, defying a wearisome tradition that extends from On the Buses right up to The Inbetweeners, the film-makers have ensured that, for her big-screen outing, Mrs Brown does not travel to the Costa del Packet and does not end up staying in a half-finished hotel.

Aside from that, the film suffers from all the ailments that plagued film adaptations of situation comedies throughout the 1970s. It is overstretched, underwritten, sluggishly paced and unsettled by the discombobulating move from studio to location.

We hardly need to say that the plot involves an evil developer who, assisted by mildly offensive Russian hoods, seeks to seize Mrs Brown’s stall on Moore Street and develop something large and hideous in its place. Meanwhile, Agnes needs to track down the receipt for an ancient tax transaction to prove that she does not owe the authorities some millions of euro. This process involves the deployment of deeply unamusing blind ninjas and moth-eaten jokes involving a barrister with the aforementioned Tourette’s. (Robert Bathurst does manage a convincingly tweedy King’s Inns drawl.).

For the first hour, raw energy and brazen goodwill holds the rickety construction aloft. But even the series’ most ardent fans may find the closing chase sequences absurdly overextended and exhaustingly pointless.

It’s all a terrible shame. The light entertainment traditions of the pre-alternative age are worth preserving. O’Carroll has heavenly timing and knows his way around grotesque drag.

Moreover, socially and politically, D’Movie does have its heart very much in the right place: eulogies to inclusion, tradition and open-mindedness pepper the dialogue. But, Jesus, Mary and Joseph, the gags are clunky, the dialogue is leaden and the story is threadbare.